The present disclosure relates generally to a fluid valve and, more particularly, to a valve assembly for controlling and shutting off fluid flow. Even more particularly, the present disclosure relates to a valve assembly having a flapper with a dynamic circumference seal.
A butterfly, or xe2x80x9cflapperxe2x80x9d valve generally includes a circular, thin flapper-plate coaxially disposed inside a fluid passageway. A rotatable shaft extends laterally into the passageway and is secured to the flapper plate. Examples of flapper valves are show in U.S. Pat. Nos. 5,485,542 and 5,564,679, which are assigned to the assignee of the present disclosure.
Rotating the shaft, accordingly, causes the flapper plate to be oriented with respect to the passageway so as to control fluid flow there through. The flapper plate is dimensioned, so that when the shaft is rotated until a plane of the flapper is oriented substantially perpendicular to a longitudinal axis of the passageway, the flapper plate assumes a fully closed position and more or less seals the passageway to stop or at least substantially reduce fluid flow. Rotating the shaft until the plane of the flapper is oriented substantially parallel to the longitudinal axis of the passageway, causes the flapper plate to assume a fully opened position. Varying rates of fluid flow through the valve can be permitted depending upon the rotational position of the flapper plate between the fully opened and the fully closed positions.
Some flapper valves have been developed to control rates of fluid flow, in which case the flapper plate need not provide a complete seal in the closed position. Certain other valves, however, are designed to provide a complete shut-off of fluid flow, in which case the circumference of the flapper plate needs to provide a complete seal with the wall of the passageway of the valve.
For a number of reasons, maintaining tight tolerances between the flapper and the inner wall of the passageway can be difficult. In both types of valves, individual parts including the body in which the passageway is formed and the flapper plate are typically made of metal and machined as closely as possible to design dimensions. In shut-off valves, the flapper plate is further provided with a solid, relatively incompressible o-ring around its circumference to provide a complete seal with the wall of the passageway of the valve.
The use of such circumferential o-rings, however, can result in an increase in the force required to rotate the shaft of the flapper valve, and can limit the speed at which the valve can be operated. In addition, operating at relatively high temperatures can result in thermal expansion of the o-rings, thereby increasing the force requirement and decreasing the operational speed. Furthermore, chemistry, pressure and temperature incompatibility of o-ring material can create short life cycles for the o-rings.
The requirement of tight tolerances is especially acute in semiconductor manufacturing, wherein process gases are being controlled at relatively high pressures, at very low rates, and wherein very low conductance at shut-off is required. What is still desired, therefore, is a flapper valve that provides very low conductance at shut-off, even between high pressure differentials, without a significant increase in the force required to operate the flapper valve.
The present disclosure, accordingly, provides a valve assembly including a valve body defining a passageway having a longitudinal axis, and a rotatable shaft extending through the body and into the passageway, generally perpendicular to the longitudinal axis of the passageway. A flapper is secured to the shaft within the passageway and movable upon rotation of the shaft between an opened position and a closed position. In the opened position, a plane of the flapper is parallel to the longitudinal axis of the passageway such that allowable fluid flow through the passageway is at a maximum. In the closed position, the plane of the flapper is perpendicular to the longitudinal axis of the passageway, such that fluid flow through the passageway is substantially prevented.
The flapper includes a groove in an outer circumference of the flapper, and an annular seal is received in the circumferential groove. The seal has an outer circumference greater than the outer circumference of the flapper so that the entire outer circumference of the seal contacts a wall of the passageway when the flapper is moved to the closed position. The seal also has an inner circumference greater than an inner circumference of the groove of the flapper such that a space is defined between the inner circumference of the seal and the inner circumference of the groove. The assembly further includes an aperture communicating with the space, such that the seal can be compressed further into the groove when the flapper is moved to the closed position.
According to one aspect of the present disclosure, the seal is metal.
According to another aspect, the seal is continuous, and the aperture providing communication with the enclosed space extends through the flapper.
According to a further aspect, the seal is discontinuous and the aperture providing communication with the enclosed space is defined between ends of the seal.
The valve assembly of the present invention is designed to provide both control and shut-off functions. In particular the assembly is designed to control pressure across a wide dynamic range by reducing the closed conductance through the passageway, and provide sufficient position resolution near the closed position of the flapper to allow controlling this reduced conductance. The presently disclosed valve assembly is also designed to be compatible with a wide array of process chemistries and temperatures, last hundreds of thousands of cycles, and be easily replaced in the field. The valve assembly according to the present disclosure provides all these benefits, yet has a relatively simple design including fewer components that are easier to assembly together during manufacturing.
These and other features and benefits of the present disclosure will become more apparent upon reading the detailed description in combination with the drawings.